1. Field of the Invention
The present invention relates to an ultrasonic linear motor using an ultrasonic transducer, and particularly to an ultrasonic linear motor with a simple configuration which enables miniaturization thereof.
2. Description of the Related Art
In recent years, ultrasonic motors have received much attention as new motors replacing electromagnetic motors. The ultrasonic motors have the advantages described below as compared with conventional electromagnetic motors.                (1) Low speed and powerful thrust can be obtained without gears.        (2) The retentivity is great.        (3) The stroke is long, and high resolution is obtained.        (4) Excellent quietness.        (5) The linear motor does not generate magnetic noise, and is not affected by noise.        
As conventional linear ultrasonic motors having the above-described advantages, an ultrasonic transducer and an ultrasonic linear motor using an ultrasonic transducer proposed by the present assignee, disclosed in Japanese Unexamined Patent Application Publication No. 7-163162, for example, is known. Description will be made below regarding the conventional ultrasonic linear motor proposed in the aforementioned Japanese Unexamined Patent Application Publication No. 7-163162 with reference to the drawings.
FIGS. 18 and 19 are diagrams for describing an example configuration of the conventional ultrasonic linear motor, and FIG. 18 is a disassembled perspective view of the principal components, illustrating the basic components of the ultrasonic transducer used in the ultrasonic linear motor in detail. FIG. 19 is a plan view which illustrates the ultrasonic transducer.
First of all, the configuration of the ultrasonic transducer will be described.
As shown in FIG. 18, a conventional ultrasonic transducer 50 used in the above-described proposed ultrasonic linear motor includes a layered piezoelectric device 50A having a configuration wherein multiple thin piezoelectric sheets 51 in the shape of a rectangle are layered, and piezoelectric sheets 52 and 53 without electrodes as insulators are layered on the top and the bottom of the layers so as to hold the layered piezoelectric sheets 51 therebetween. Furthermore, the layered piezoelectric device 50A has a configuration wherein internal electrodes 54a and internal electrodes 54b are alternately inserted between each piezoelectric sheet.
The internal electrodes 54a and 54b of the piezoelectric sheet 51 are provided on the upper-half region of thereof. While the internal electrodes 54a are formed so as to extend up to the side end portions of the transducer (piezoelectric sheet 51), the internal electrodes 54b are formed so as to extend up to the top face end portion of the transducer (piezoelectric sheet 51).
The piezoelectric sheets 51 and the internal electrodes 54a and 54b are positioned on the green sheet of lead zirconate titanate (which will be referred to as PZT hereafter) by being printed electrodes thereon, and are baked in the layered state, whereby a layered piezoelectric layered device 50A is formed. Note that, with the layered piezoelectric sheets 51, 52, and 53, the internal electrodes 54a are exposed on the side face portions, and also the internal electrodes 54b are exposed on the upper side portion, in the configuration described above.
With the ultrasonic transducer 50 configured using the layered piezoelectric device 50A having the above-described configuration, external electrodes 55 made up of conductors are provided at the positions where the internal electrodes 54a are exposed on both side portions of the layered piezoelectric device 50A, i.e., one each of the left and the right sides serving as grounds (GND), and the positions where the internal electrodes 54b are exposed on the upper portion of the layered piezoelectric device 50A, i.e., two portions on the top face serving as input A and input B, as shown in FIG. 19.
Here, with the ultrasonic transducer 50, the electrode terminal wherein the external electrode 55 is connected to the internal electrodes 54b extended from the left side of the upper face portion of the layered piezoelectric device 50A will be called as A (input A), the electrode terminal wherein the external electrode 55 is connected to the internal electrodes 54b extended from the right side of the upper face portion of the layered piezoelectric device 50A will be called as B (input B), and the electrodes 55 disposed on both side face portions of the ultrasonic transducer 50 are grounds (GND).
Furthermore, leads are each connected to the external electrodes 55 with solder or the like, which is not shown in the drawings, and these leads are connected to an unshown driving circuit for the piezoelectric sheets 51.
Protruding driving elements 56 are also provided at predetermined positions on the bottom face of the layered piezoelectric device 50A, and are pressed into contact against an unshown driven member for sliding (moving with friction) the driven member. The driving elements 56 are provided at arbitrary positions where the ultrasonic transducer 50 performs elliptic vibration.
Furthermore, a small through hole is provided at the center portion of the ultrasonic transducer 50, and a pin 57 is mounted through the through hole.
In order to configure and operate an ultrasonic linear motor using the ultrasonic transducer 50 having the above-described configuration, pressing means for engaging the pin 57 and pressing the driving elements 56 in the lower direction in the drawing, and a driven member which is pressed into contact against the driving elements 56 of the ultrasonic transducer 50, are provided so as to be relatively moved to the driving elements 56, whereby the ultrasonic linear motor is configured.
Note that the driven member is held by a linear guide, which is not shown in the drawings, and can be linearly moved by being pressed into contact against the driving elements 56 and being guided by the linear guide.
Next, operations of the above-described ultrasonic transducer 50 will be described.
With the ultrasonic linear motor using the ultrasonic transducer having the above-described configuration, a direct current voltage (DC voltage) is applied to the external electrode 55 through unshown leads so that polarization is effected.
Furthermore, upon applying AC voltages (with frequency which is the resonance frequency for the ultrasonic transducer 50), wherein the phase of one AC voltage is different from another by π/2, to the above-described input A and input B, first longitudinal vibration and second flexural vibration are generated at the portions of the driving elements 56, thereby enabling clockwise or counterclockwise ultrasonic elliptic vibrations to be generated. At this time, due to generating of the ultrasonic elliptic vibration, the driven member which is pressed into contact against the driving elements 56 can be driven in the right direction or the left direction, and thus the arrangement can serve as an ultrasonic linear motor.
On the other hand, a linear ultrasonic actuator disclosed in Japanese Unexamined Patent Application Publication No. 9-19172 is another known example of conventional art. The proposed linear ultrasonic actuator will be described with reference to FIG. 20.
FIG. 20 is a disassembled perspective view which illustrates a schematic configuration of the proposed conventional linear ultrasonic actuator.
As shown in FIG. 20, a linear ultrasonic actuator 60 of the present example comprises a base 61, a frame member 62, side plates 63, guide members 65, top face plates 66, a transducer 68, elastic members 69, movable rails 70, a table 71, mats 72, double-faced adhesive tapes 73, and so forth.
The transducer 68 is vertically held between a pair of elastic members 69, and is positioned on the base 61 through a seat plate (not shown), and electrodes connected to high frequency electrodes are formed on the top face and bottom faces thereof, which is not shown in the drawings. Furthermore, a collar having a flange-shaped portion on the upper portion thereof is inserted into the transducer 68, the elastic members 69, the seat plate (not shown), and the center hole of the base 61, and a stopper is mounted at the bottom end thereof, so that the base 61, the seat plate, the elastic members 69, and the transducer 68 are held between the flange-shaped portion and the base 61, which is not shown in the drawings.
A pair of the movable rails 70, which are pressed into contact against the circumference face of the transducer 68 so as to narrow the spacing thereof, and which have V-shaped grooves (not shown) extending in the entire longitudinal direction on one side thereof, are moved in the direction of A and B shown by arrows in the drawing upon applying a high-frequency voltage to the transducer 68. The table 71 connecting the one pair of movable rails 70 is mounted to the movable rails 70 with the double-faced adhesive tapes 73, with a mat 72 made up of a elastic member introduced therebetween.
The above-described configuration aims to provide a linear ultrasonic actuator wherein stable linear actions can be obtained.